Final answer:
If you receive a "No CAT II" message below 300 ft. AGL while flying, it means that the Category II Instrument Landing System approach is not available for landing. Pilots usually perform a missed approach or divert to an alternative airport.
Step-by-step explanation:
If you receive a "No CAT II" message below 300 ft. AGL (Above Ground Level) while flying, it means that the Category II Instrument Landing System (ILS) approach is not available to use for landing. CAT II is a higher level of precision approach that requires special pilot training and specific equipment on the aircraft. When this message appears, pilots typically need to perform a missed approach or proceed to an alternative airport where a CAT II approach is available.